Flexible metal tape suitable for use in tubing and electrical cable shields and having at least one of its sides coated with a copolymer of ethylene and a monomer having a reactive carboxyl group, such as disclosed in U.S. Pat. No. 3,795,540, are well known in the art. Examples of an 8 and 12 mil aluminum tape coated on both sides with approximately 2 mils of a copolymer of ethylene and a monomer having a reactive carboxyl group suitable for use in the present invention are respectively sold under part numbers A282 and XO-5554.07 under the Trademark "Zetabon" by Dow Chemical Company.
Examples of shielded electrical cable or tubing utilizing metal tapes having the previously described adhesive on one or both of its sides are disclosed in U.S. Pat. Nos. 3,233,036; 3,272,912; 3,332,138 and 3,379,821. Such tapes proportedly provide mechanical protection and electrical shielding characteristics and such coating proportedly provides the metal with improved resistance to corrosion and, where spiralled or longitudinally folded into a tubular form and suitably bonded the overlap, are able to provide an effective gas and moisture barrier. The presence of a reactive carboxyl group in the ethylene copolymer coating proportedly enhances chemical bonding in a moist corrosive atmosphere and enables polyolefinic materials, such as polyethylene, to be effectively bonded to the tape.
Although metallic tapes having at least one side coated with a copolymer of ethylene and a monomer having a reactive carboxyl group may be used to advantage in products such as disclosed in the previously described references, it has been found that flexible or semi-rigid non-olefinic amorphic polymers such as polyvinyl chloride and polyurethane and substituted polyolefins such as halogenated polyethylene of which an example is chlorinated polyethylene and chlorosulfonated polyethylene such as sold under the trademark Hypalon being E. I. DuPont de Nemours do not bond well to the ethylene and monomer copolymer coating and as such have heretofor been unable to be used in conjunction with such tapes in an adhesively bonded relationship.
There are many instances in both tubing and electrical cable shielding where it is desirable to bond flexible or semi-rigid non-olefinic polymeric materials directly to the ethylene and monomer copolymer coating and thereby bond the metal tape to such polymers in order to utilize the greater flexibility and other desirable characteristics generally associated with such polymers and to minimize or eliminate wrinkling of such polymers upon the bending of tubing and electrical cable products in which they are used. Since flexible and semi-rigid non-olefinic polymeric materials in general are able to be effectively compounded for flame retardancy and remain more flexible than similiar compounds made from olefinic polymers, such as polyethylene and polypropylene, the present invention also provides a method by which flexible or semi-rigid flame retardant non-olefinic polymeric materials, such as polyvinyl chloride, are able to be bonded to flexible metal tapes coated with a copolymer of ethylene and a monomer having a reactive carboxyl group to provide tubing and shielded electrical cable that features enhanced flame retarding characteristics in combination with improved flexibility in conjunction with improved resistance to wrinkling of such materials upon the bending of products utilizing the combination.
More particularly, it has been found that flexible or semi-rigid non-olefinic polymeric materials that heretofor have been unable to be satisfactorly bonded to metal tapes coated with a copolymer of ethylene and a monomer having a reactive carboxyl group can be effectively bonded indirectly thereto by the use of an adhesive deposed between the coating and such materials that is adapted to bond them together. It has been further found that a polyamide based adhesive is particularly advantageous in bonding a broad range of flexible or semi-rigid non-olefinic polymeric materials to such coated tapes.
As used herein, the term "non-olefinic polymeric materials" means olefinic polymers such as polyethylene and polypropylene in which a sufficient number of the available hydrogens have been replaced within the carbon chain and/or pendant thereto with chemical groups such as nitrogen or halogens such as chlorine or fluorine and the like to cause them to be classified as either non-olefinic or amorphic or elastomeric in nature rather than polyolefinic and includes elastomers such as chlorosulfonated polyethylene and elastomers such as polyurethane that contain closed carbon rings in their structure. As such, the term "non-olefinic polymeric materials" includes amorphic polymers such as polyvinyl chloride in which certain of the pendant hydrogen atoms pendant to the olefins carbon chain backbone have been replaced with chlorine atoms as is also the case for polymers such as elastomeric chlorinated polyethylene and also includes polymers such as nylon in which nitrogen atoms are used within the carbon chain backbone as well as elastomers such as chlorosulfonated polyethylene which feature substitutes of both chlorine and sulfur atoms for hydrogen atoms pendant to the olefinic carbon chain backbone.